This is a really cool bit of behaviour that I filmed on a dive to Pinnacles on Two Mile reef while we were in Sodwana last September, and one of my favourite things of all that we saw. A malabar rockcod (Epinephelus malabaricus) – as identified by our dive guides – in dark hunting colours, patrols the reef ahead of a honeycomb moray (Gymnothorax favagineus). At the time I didn’t know what was happening – it looked as though the eel was stalking the grouper – but it turns out to be more complicated and more interesting than that. I had filmed a subset of a total pattern of behaviour, in which the moray and rockcod (from the family of fish also called grouper) were hunting co-operatively.
[youtube=”https://www.youtube.com/watch?v=YzU9_cRW97E&w=540″]
A researcher at a Swiss university discovered in 2006 that coral groupers seek out giant moray eels (both of these species live in the Red Sea), summoning the eels from their dens with a vigorous shaking of their bodies. The fish and the eel then swim together looking for prey , a deadly tag-team of hunters. The groupers are fast in open water, but the eel can get into crevices to flush out prey. It is this behaviour, executed by a different type of eel and a different type of grouper, that I saw in Sodwana.
The scientists reported that the groupers use a head-stand signal, combined with a shaking of their bodies, to indicate the location of hidden prey to the eels. When the eels see this, most of them swim towards the grouper, and flushed out the prey.
You can read more about the study that revealed the extent of this behaviour here, and the actual paper reporting the research here. The scientists also discovered two other species with complementary skills that hunt co-operatively, on the Great Barrier Reef this time: the coral trout, and octopus.
Moray eels look incredible when they swim freely across the reef. Here’s one doing just that, in the Red Sea.
